This invention relates to an energy absorbing device suitable for use alongside a roadway to decelerate an impacting vehicle.
Roadside energy absorbing devices have in the past used many approaches to create a retarding force tending to slow an impacting vehicle. Inertial barriers rely on the dispersion of a mass of material such as sand, as described for example in U.S. Pat. Nos. 29,544 and 4,934,661. Other prior art systems have used containers of a liquid such as water which is forced through one or more orifices in an impact to create a retarding force (U.S. Pat. No. 3,672,657). Another approach is described in U.S. Pat. No. 4,352,484, in which a foam filled grid is forced through an adjacent foam filled grid in an impact. Other prior art devices have relied on the deformation of metallic elements by bending (U.S. Pat. Nos. 4,711,481 and 3,211,260) and on frictional forces generated between brake elements and a cable (U.S. Pat. No. 5,022,782).
In the last named of these systems, a cable is oriented along the axial direction, and an impacting vehicle forces a brake assembly to move along the cable. This brake assembly includes disc springs that press aluminum brake shoes against the cable to create a retarding force. This force is largely generated as a result of friction, though the aluminum is abraded during the process as well.